1. Field of the Invention
The present invention relates to a photographic element having a neutralizing system for a color diffusion transfer process (DTR color) and particularly to a photographic element for DTR color comprising a novel timing layer.
2. Description of the Prior Art
Hitherto, it is well known in the color diffusion transfer process to provide a neutralizing layer in order to decrease the pH after transferring diffusible dyes or dye developing agents to a mordanting layer as a result of development using an aqueous alkaline developing solution.
However, if the pH is rapidly decreased by providing a neutralizing layer, the development is interrupted. In order to prevent such a defect, it is also well known to utilize a layer which controls the reduction of the pH with time, namely a "timing layer", together with the neutralizing layer.
A neutralizing system containing these layers can be divided into two types, one type having a timing layer in which the water permeability is inversely proportional to the temperature and the other type having a timing layer in which the water permeability is directly proportional to the temperature.
The term "water permeability" used herein means the property of substantially passing an aqueous alkaline developing solution therethrough. More specifically, when a pH indicator (Thymolphthalein) coating film as described in Example 3 hereinafter is placed face-to-face with a timing layer on a neutralizing layer and an alkaline viscous solution is spread between them, where the pH indicator coating film becomes colorless, the timing layer is defined as being water permeable.
In using a timing layer in which the water permeability is inversely proportional to the temperature, the period of time at a high pH (preferably, a pH of about 10 or more) for developing silver halide and forming an imagewise distribution of diffusible dyes increases as the temperature increases. A neutralizing system having a timing layer which is temperature dependent is fundamentally suggested in British Pat. No. 1,071,087. Further, materials for the timing layer include polyvinyl amide type polymers described in U.S. Pat. Nos. 3,421,893 and 3,575,701. A neutralizing system having a timing layer wherein the above-described materials are used where the period of time at high pH increases as the temperature increases is advantageously utilized for the color diffusion transfer process which has the disadvantages that the development rate or the diffusion rate of the dye developing agent is high and excessive amounts of dyes are adsorbed in the mordanting layer at low temperatures, such as the color diffusion transfer process described in U.S. Pat. Nos. 2,983,606, 3,415,644 and 3,415,645.
On the other hand, a neutralizing system having a timing layer in which the water permeability is directly proportional to the temperature where the above-described period of time at a high pH decreases as the temperature increases is advantageously utilized for the color diffusion transfer process which uses dye image forming materials which are not diffusible initially but release a diffusible dye as a result of an oxidation-reduction reaction or a coupling reaction thereof with an oxidation product of the developing agent (hereinafter, materials of the former type are called "DRR compounds" and materials of latter type are called "DDR couplers") as described in U.S. Published Application B351,673, U.S. Pat. Nos. 3,929,760, 3,931,144 and 3,932,381. Namely, the delay of the development of silver halide and the delay of the above-described oxidation-reduction reaction at a low temperature and the deterioration of densities of transferred color images caused by the delay of the diffusion of dyes can be corrected by prolonging the period of time at high pH (namely, prolonging the period of time where developing of silver halide and releasing and transferring of the dyes can occur).
Examples of timing layers where the water permeability increases as the temperature increases are timing layers composed of polyvinyl alcohol as described in U.S. Pat. No. 3,362,819, layers described in U.S. Pat. No. 3,785,815, layers described in Research Disclosure, p. 86 (November 1976) and U.S. Pat. Nos. 4,056,394 and 4,061,496 (namely, timing layers formed from a latex of methyl acrylate-vinylidene chloride-itaconic acid copolymers or acrylonitrile-vinylidene chloride-acrylic acid copolymers), layers composed of a latex of styrene-butyl acrylate-acrylic acid copolymer as described in Japanese Patent Application (OPI) 72622/78 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application") and layers composed of a latex of styrene-butyl acrylate-acrylic acid-glycidyl acrylate copolymers as described in U.S. Pat. Application Ser. No. 966,407.
However, in the timing layers described in U.S. Pat. No. 3,785,815, the delay in development cannot be sufficiently compensated for, because the degree of the decrease in water permeability in the low temperature range is small. Where the timing layers described in Research Disclosure, supra on U.S. Pat. Nos. 4,056,394 and 4,061,496 are used, the delay in development can be sufficiently compensated for, because the water permeability in the low temperature range can be sufficiently delayed. However, since these timing layers are produced by coating polymer latexes and drying, the difficulties which polymer latexes inherently have are encountered in the production of these timing layers. That is, in order to obtain a transparent layer from a polymer latex, it is necessary to dry a polymer latex layer coated at a temperature above a minimum film forming temperature which is determined depending on the softening temperature of polymer particles which compose the polymer latex layer. Therefore, the use of polymer latex which has a low minimum film forming temperature is desired in order to economize cost of fuel in the production of a timing layer. However, when a polymer latex having a low minimum film forming temperature is used, due to the low softening point of the polymer, the timing layer causes blocking between the timing layer and a back surface of the film when the film having the timing layer is rolled or the timing layer causes a blocking defect between the timing layer and a surface of a light-sensitive film after the formation of a DTR color photographic film unit. Thus, a timing layer should be produced using a polymer latex having a high minimum film forming temperature (a high softening temperature) in order to prevent such blocking defects. Where a polymer latex having a high softening temperature is used, a method of drying at a high temperature or a method in which a solvent being capable of dissolving to some extent the polymer is admixed with the polymer latex and drying is carried out at a low temperature with the assistance of a film formation accelerating effect of the solvent used (the solvent used is designated "film formation assisting solvent" hereinafter) are well known in the polymer latex field. However, in the former method the cost of fuel for drying is high and in the latter method a hazardous vapor is generated during the manufacture thereof because of using the solvent and the cost of production increases for the solvent.